The present invention relates to a photopolymerization initiator, a photopolymerizable initiator composition, a photosensitive colored composition for producing a color filter used in a color liquid crystal display element and a color solid image pickup element, and a color filter and a liquid crystal display element using the same.
A polymerization method in which light is applied in the presence of a photopolymerization initiator when a monomer or oligomer having a polymerizable unsaturated group such as a vinyl group is polymerized to cure the paint film has the advantages that the curing speed is fast as compared with those in other methods and curing at a low temperature is possible, and therefore it is widely used for paints and resists. The curing speed depends on a photopolymerization initiator, and therefore various photopolymerization initiators have so far been developed.
German Patent 1694149, for example, discloses benzoin ethers. In addition thereto, photo radical-generating agents such as allyl diazonium salts and halogenated hydrocarbons are known. Further, it is known that certain organic peroxides are useful as a photopolymerization initiator, and that a lot of investigations on these polymerization systems have been made. Specifically, aromatic compounds having a specific t-butyl peroxyester are disclosed in U.S. Pat. Nos. 4,171,252, 4,416,826 and 4,752,649.
Further, synthesis of benzophenone derivatives having one to two peracid esters, such as 4,4xe2x80x2-di(t-butyl peroxycarbonyl)benzophenone and polymerization of vinyl monomers are investigated in Journal of Organic Chemistry, vol. 44, p. 4123 (1979) and Journal of Polymer Science Chemistry, vol. 21, p. 3129 (1983).
Among these compounds, however, those having one peracid ester have had the defect that the photopolymerization activity is low, while those having two peracid esters have had the defects that crystals are liable to precipitate during cold storage after being diluted and dissolved in organic solvents and that the raw materials are expensive and the production cost is high.
A benzophenone derivative having four peracid esters, disclosed in Japanese Patent Publication No. 60322/1991, has a good photopolymerization activity and is inexpensive in terms of a raw material, but it has the defect that crystals precipitate during cold storage after being diluted and dissolved in an organic solvent.
Further, peracid esters disclosed in Japanese Patent Application Laid-Open No. 17547/1998 have a high sensitivity and do not precipitate as crystals while they are kept in cold storage after being diluted and dissolved in an organic solvent. However, they are defective in that the production process is long and involves reactions difficult to carry out, thus leading to a high production cost.
As described above in detail, an object of the present invention is to provide a photopolymerization initiator which has a high sensitivity and is inexpensive and in which precipitation of crystals does not occur when kept in cold storage after being diluted and dissolved in an organic solvent.
A further object of the invention is to provide a photopolymerizable initiator composition using this photopolymerization initiator, a photosensitive color composition and a color filter.
That is, the first aspect of the present invention is a photopolymerization initiator represented by the following Formula (1): 
wherein R1 and R2 represent independently a tertiary alkyl group having 4 to 15 carbon atoms or a tertiary aralkyl group having 9 to 15 carbon atoms; X1 and X2 represent independently xe2x80x94Oxe2x80x94 or xe2x80x94NHxe2x80x94; R3 represents an organic group having 1 to 30 carbon atoms in which an atom bonded to X1 is not an oxygen atom; and R4 represents an organic group having 1 to 30 carbon atoms in which an atom bonded to X2 is not an oxygen atom, a tertiary alkoxy group having 4 to 15 carbon atoms or a tertiary aralkyloxy group having 9 to 15 carbon atoms.
The preferred embodiment is a case where xe2x88x92X1xe2x88x92R3 and xe2x88x92X2xe2x88x92R4 in Formula (1) represent independently an alkoxy group which is an alcohol residue of methanol, ethanol, 2-propanol, 1-butanol or benzyl alcohol, a case where they represent independently an alkoxy group which is an alcohol residue of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate or hydroxybutyl (meth)acrylate or a case where they represent independently an alkoxy group which is an alcohol residue of dimethylaminoethanol or diethylaminoethanol.
The second aspect of the invention is a photopolymerization initiator represented by the following Formula (2): 
wherein R5, R7, R8, R9, R10 and R11 represent independently a tertiary alkyl group having 4 to 15 carbon atoms or a tertiary aralkyl group having 9 to 15 carbon atoms; R6 and R12 represent independently a tertiary alkoxy group having 4 to 15 carbon atoms, a tertiary aralkyloxy group having 9 to 15 carbon atoms or an organic group having 1 to 30 carbon atoms in which an atom bonded to X3 is not an oxygen atom; X3 represents xe2x80x94Oxe2x80x94 or xe2x80x94NHxe2x80x94; R13 represents an alkylene group having 2 to 8 carbon atoms; m represents an integer of 1 to 30; and n represents an integer of 0 to 30.
The preferred embodiment is a case where xe2x88x92X3xe2x88x92R6 and xe2x88x92X3xe2x88x92R12 in Formula (2) represent independently an alkoxy group which is an alcohol residue of methanol, ethanol, 2-propanol, 1-butanol or benzyl alcohol, a case where they represent independently an alkoxy group which is an alcohol residue of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate or hydroxybutyl (meth)acrylate or a case where they represent independently an alkoxy group which is an alcohol residue of dimethylaminoethanol or diethylaminoethanol.
The third aspect of the invention is a photopolymerizable initiator composition comprising at least one photopolymerization initiator represented by Formula (1) or (2).
The fourth aspect of the invention is the photopolymerizable initiator composition described above in which at least one photopolymerization initiator other than those represented by Formulas (1) and (2) and/or at least one sensitizing dye is used in an amount of 1 to 80% by weight (hereinafter all percentages are in terms of % by weight) based on the total amount of the photopolymerization initiator(s) or the sensitizing dye(s). A preferred amount is 10 to 70%.
The fifth aspect of the invention is a photosensitive colored composition comprising the photopolymerizable initiator composition of the third invention in admixture with a coloring material.
The sixth aspect of the invention is a color filter produced by using the photosensitive colored composition described above.
The seventh aspect of the invention is a liquid crystal display element produced by using the color filter described above.